glasmachers



3 Sheets-Sheet 1.

(No Model.)

G. GLASMAUHERS.

BLAGKBOARD.

No. 603,631. Patented May 10,1898.

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3 Sheets-Sheet 2. G. GLASMAGHERS.

A BLAGKBOARD. No. 603,631.

Patented May 10,1898.

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(No ModeL) 3 Sheets-Sheet.

G. GLASMAC-HERS.

BLAGKBOARD.

N0. 603,631. Patented May 10,1898.

n Nl] J/T l k E j) E E i C Enr N Wtnesses Inventor 6. Zmm I UNITEDSTATES PATENT OFFICE.

GOTTFRIED GLASMACHERS, OF. ESSEN, GERMANY.

BLACKBOARD.

SPECIFICATION forming part of Letters Patent No. 603,631, dated May IO,1898.

Application filed April 2 2 l 8 9 7.

T0 a/ZZ whom it may concern.-

Beit known that I, GOTTFRIED GLAsMAcH- ERS, a subject of Vthe Emperor ofGermany, and a resident of Essen, Prussia, Germany, have invented acertain new and useful Improvement in School-Blackboards, of which thefollowing is a specification.

v This invention relates to that class of schoolblackboards in which theboard is designed to be set higher or lower; and said invention consistsin novel devices for rendering such construction more conveniently andefficiently operable. The novel devices referred to include a boardhaving pins carried in bearingblocks guided up and down, said boardbeing suspended by helical springs having a force about equal totheweight of the board vattached to the supporting-frame, so that it may beeasily moved downward when disengaged, the lifting actionserving tocorrespondingly elevate the board when desired; but in order to carrythis into operation it is necessary to provide a board which shall notbe so heavy as the usual wooden boards.

I will describe the improved construction with reference to theaccompanying drawings in which- A Figures l and 2 are respectively afront elevation and avertical section of the board without the stand.Fig. 3 is a section, on a larger scale, showing the mode of constructingthe board with its frame. Figs. 4 and 5 are respectively a verticalsection and a front elevation of the board together with the stand. Fig.6 is a section' of portions of the board, showing the manner of itssuspension and guidance in the stand, on a larger scale. Fig. 7 is afront elevation of the same.

Like letters of reference indicate corresponding parts in the severalfigures where they appear.

The board is composed of holzlz (woodfelt or cork-felt) covered withleather-board. The two layers of leather-board B B, Fig. 3, are cementedonto the plate of felt A by means ofwater-glass, silicate of soda, orsilicate of potash. The Writing-surfaces are first impregnated with hotlinseed-oil, then coated twoor three times with a putty-like mass C C,composed of Japan lacquer and finely-reduced gray keiselguhr, aninfusorial earth of great lightness occurring liberally in Ober- SerialNo. 633,214. (No model.)

lohe in Hanover, flattened down with aspatula or painters knife, andrubbed with pumicestone and oil. The wood-felt or cork-felt plate A ischaracterized by great lightness and has the advantage that it does notwarp. The cementing together of the three plates with water-glassserves, first, to introduce the least possible amount of moisturebetween kthe plates, and, second, to aid still more in obviating warpingthe plates. The repeated varnishin g with the inf usorial earth andrubbing down adds but inappreciably to the weight and gives a strong anddurable surface, which is just sufficiently rough to receive the crayonsor other ordinary writing and marking materials. The finished plate isthen placed in the frame D, which consists of light wood.

The framing is effected by filling up the grooves of the frame withcement composed of keiselguhr and glue E and forcing the plate intightly. l In thismanner there is produced a light elastic board firmlyfixed in its frame. Right and left in the frame are carried pins G, uponwhich the board swivels. These pins rest in bearings I-I, which slide upand down in the grooves z' in the stand I.

The said bearings are suspended by helical springs J, which yield whenthe board is let down. The retention of the board is effected by meansof hooks K, arranged at the top of the frame and formed of fiat bar orstrip iron, adapted to take into suitable toothed racks I', fixed to thestand.

The suspension of the board by long-action springs allows of rapid andconvenient lifting up or letting down of the board, because the springsare always uniformly tensioned. These motions are performed without thepossibility of jamming, and all noise and jolting of the board areobviated. The

said helical springs J also have such range and length that their forceis nearly equal in all positions of the board.

When the board has been` let down below I IOO tom of the board, whichwill come into posiv tion for use when the board is inverted.

The hooks Which come at the top may be engagedin the lowermost or in anyother of the notches in the racks, according as it is desired to havethe board held high or low.

Modifications may be made Without departing from the spirit orsacrificing the advantages of the invention. Parts of the invention canbe used Without the Whole. The springs may be dispensed with, the boardbeing suiiiciently light to permit its Y Weight to be sustained by theuser during the adjustment.v

I claim asl my inventionl. A school-blackboard having a Writingsurfaceformed bya mixture of Japan lacquer and reduced keiselguhr rubbed orpolished,

'substantially as herein speciiied.

2. A school-blackboard comprising a sec; tion of wood or cork felthaving a layer ofl leather-board cemented thereto by soluble glass andfaced with a mixture of Japan lacquer and reduced leiselguhr in two ormore layers, rubbed or polished, substantially as4 herein specified.

3L In a school-blackboard, the combination' of a plate A of Wood-felt orcork-felt, which is covered with two leather-boards cemented thereto bymeans of Water-glass under the application of pressure, upon whichboards B, B, the Writing-surfaces C C are formed of layers of Japanlacquer and keiselguhr, the

iWhole being firmly Xed in a Wood frame D, 'substantially as hereinspecified.

4. In a blackboard, the Within-described board A B, D, mounted by meansof the pins G, in bearings II, Which latter are guided in grooves. Q1 ofthe stand I, and suspended by means of contractile helical springs J,Whereby the Weight of the board is approximately ,balanced and itsraising and lowering is more easily eected, in combination with thehooks and toothed racks for engaging said board, all arranged for jointoperation, substantially as herein specified.

In testimony whereof I have hereunto set my hand, at Essen-on-the-Ruhr,this 7th day kof April, 1897, in the presence of two subscribin gWitnesses.

GOTTFRIED GLASMACHERS; Witnesses:

LANWOR LIEBER, WM. EssENWEiN.

